1. Field of the Invention
This invention relates to key actions for power driven typewriters and more particularly to a coupling arrangement between a keylever and an interposer.
2. Description of the Prior Art
A simple reliable key action is a vital necessity for the manufacturer of an economical quality typewriter. The key actions employed for use in contemporary typewriters must be capable of withstanding the increasing frequent demands required of such modern machines. Combine that factor with a need for producing key actions at the lowest possible cost to the manufacturer brings together an achievement long sought by the typewriter industry, namely a reliable, low cost structure. Electric typewriters having typebars include a significant number of individual key actions (normally at least 42), it is readily apparent that, any simplifications effecting the key action results in a substantial reduction of the total cost. A prime example of such a simplification effecting cost is to educe the number of moving parts required for each key actioh, which in turn significantly decreases the total number of typewriter parts. Accordingly, a further cost savings is realized as a result, because the required assembly and labor time is similarly reduced. In many prior art key actions, critical moving parts require at least one and for some several bend forms. These have the disadvantage of being both costly and complex, they require a precise manufacturing operation for obtaining the form and for proper function must be inspected. Once assembled, formed parts tend to obscure other parts, complicating trouble shooting and part replacement. To avoid these problems it is most desirable and economical to employ parts having a flat blank construction. By simplifying the key action, costly critical assembly adjustments requiring skilled personnel are minimized or avoided. The use of fewer moving key action parts reduces future repair and part replacement due to failure or wear.
An example of a simplified key action arrangement in a typewriter is U.S. Pat. No. 1,077,281. The key action includes a keylever directly connected to and vertically aligned with one arm of a two armed rocking lever. The other arm of the rocking lever is connected to a sliding link which in turn is connected to a typebar. The direct connection between the keylever and the rocking lever includes a recess on the keylever which fits into a circular end portion on one of the arms of the rocking lever. The other arm of the rocking lever is similarly shaped and fits within a recess on the sliding link. The sliding links are bent each a different amount for alignment with their corresponding typebar. This key action arrangement is possible because it is used in a manual typewriter.
In most conventional powered key actions having a continually driven power roll or toothed snatch roll, a pawl or cam is pivotally mouned on an actuator or sublever for displacement into driving engagement with the rotating power roll in response to keylever depression. As a result of such a driving engagement, a typebar is caused to perform a printing stroke.
In these conventional key actions, there is normally provided a mechanism operatively connecting the keylever with the pawl or cam for producing a reliable key action function. Usually included within such mechanisms is an intermediate lever or interposer that moves in response to keylever depression. A prior art key action U.S. Pat. No. 3,915,277 issued Oct. 28, 1975 to Samuel D. Cappotto et al, as inventor and assigned to the same assignee as the present application, discloses a horizontal interposer being spring loaded against a bellcrank that is pivotally connected to a keylever. Depression of the keylever will increase the spring tension applied to the interposer by pivoting the bellcrank until the interposer is pushed off a ledge by the descending keylever. The stretched spring will then snap the interposer against a pawl that engages the power roll to initiate the printing movement of the typebar.
The Cappotto et al patent is an improved key action, in that it provides for rapid insertion of the pawl into the path of rotating teeth on the power roll upon keylever depression. The mechanism contains many moving parts for operation of the interposer, namely a bellcrank pivotally mounted on a pin to a keylever. Such structure has the disadvantage of being both complex and costly to manufacture. The construction also requires a spring that must be individually connected to each interposer and bellcrank, thus further complicating the key action. Each keylever used in the Cappotto key action is formed with an ear, requiring the disadvantage of an additional costly manufacturing operation. A finger on the bellcrank is spring loaded against the interposer and a keylever ear slides against the interposer subjecting the parts to undesirable frictional wear. Such key action complexities and cost are severely compounded, when applied to a typewriter having a large number of such individual mechanisms.
Other prior art key actions still fall short of the optimum requirements for a key action. Many prior art key actions include a bellcrank pivotally mounted on the keylever. The bellcrank is spring biased for actuation of the interposer when the keylever is depressed and yieldably permitting the interposer to completely restore after a single typing operation. Other key action mechanisms include parts that must be adjusted for controlling the driving engagement between the cam and the power roll to vary typebar impression. The design structure of the present invention avoids the above design complexities and thereby reduces the manufacturing cost.